Question 785103
let the rate with which trucker traveled the first 300 mi be s mph.
Now, the Time = {{{Distance / speed}}}
time taken for 300mi + time taken for 240 mi = 16 hours
{{{300/s}}} + {{{240/(s+10)}}} = 16
which becomes
16{{{s^2}}} -380s -3000 = 0
Solving this quadratic equation 
*[invoke quadratic "x", 16, -380, -3000 ]
Neglecting the negative solution we get s = 30mph.